This invention relates to novel dioxolane compounds. More particularly the invention relates to dioxolane compounds useful as photopolymerization initiators and to photopolymerizable compositions of matter containing such compounds.
Polymerization induced by the exposure of monomers to high levels of ultraviolet radiation has been known for many years. The prior art also teaches that the levels of ultraviolet radiation required to initiate polymerization may be reduced by the use of various compounds known as photoinitiators. Such compounds, upon exposure to ultraviolet light of appropriate wave length, provide a source of free radicals which induce polymerization of the monomers present.
Photoinitiators may be generally divided into two categories; namely, those which initiate polymerization when exposed to short wave ultraviolet radiation (less than 280 nm), and those which initiate polymerization only upon exposure to ultraviolet light of longer wave length on the order of 280 to 340 nm.
Photopolymerizable compositions for medical, dental, cosmetic and other applications to the human body must cure effectively upon exposure to long wave ultraviolet radiation because short wave ultraviolet radiation is dangerous to humans. Accordingly, a photoinitiator effective to induce polymerization and hence to induce cure of the composition after the shortest possible exposure to ultraviolet radiation is preferred. In addition, the photoinitiator should be effective at low concentration to preclude objectionable modification of the cured composition. The initiator must also be nontoxic to preclude adverse biological reaction such as dermatological or allergenic irritation or sensitization. Relatively minute concentrations of a biologically unacceptable photoinitiator may cause both irritation and sensization; hence even a low concentration of such a photoinitiator is precluded in photopolymerizable compositions to be applied to the human body.
Low photoinitiator concentration is also preferred in photopolymerizable compositions for industrial applications. Only those photoinitiator molecules near the surface of an applied photopolymerizable composition may react to produce free radicals. The residual photoinitiator molecules act as a diluent in the polymerized composition, migrate to its surface leaving voids which adversely affect its structural properties, and are otherwise objectionable. The problem may be serious when the photoinitiator is present, as it frequently is, in high concentrations up to 30% of the weight of the composition.
It is accordingly one object of this invention to provide novel dioxolane compounds useful, inter alia, as photoinitiators which are effective in relatively low concentration and upon the application of long wavelength ultraviolet radiation. A further object of the invention is to provide novel dioxolane compounds of which at least the embodiments do not irritate or sensitize human tissue. It is a further object of the invention to provide photopolymerizable compositions, including compositions for medical, dental, and cosmetic application, which contain such novel photoinitiators, as well as polymerized or cured, products formed from such compositions.